1. Field of the Invention
The invention relates to a printing apparatus which reduces a difference of picture quality between a deteriorated image and a non-deteriorated image to obtain a print result in which a boundary between the deteriorated image and the non-deteriorated image is inconspicuous.
2. Related Background Art
In recent years, an information processing system has been generalized and widely used. In such a situation, many electronic documents are formed on the information processing system, there is a tendency such that an output request to a color printing apparatus is increasing, and a high-speed color printing apparatus of a low cost is demanded.
Hitherto, in a print system for interpreting a page description language (PDL) transmitted from a host computer or a print server and forming a raster image, generally, the PDL is interpreted, thereafter, a display list (DL) as an intermediate language is formed, and raster image conversion (rendering) from the DL is executed.
At this time, since a size of the PDL data is not limited, there is a case where a size of DL which is formed from the PDL data is very large. If the DL is complicated and its size increases, a work area which is used by a renderer for rendering the DL also increases.
However, since an amount of memory which is provided in the printing apparatus is limited and there is a limitation of costs, in many cases, there is not a memory capacity enough to store the DL.
Therefore, a size of area to store the DL and a size of work area which can be used by the renderer are limited and there is a limitation such that a DL of a predetermined size or more cannot be processed.
A process called a fallback is executed to avoid such a limitation. According to the fallback, when the size of DL exceeds the predetermined size or if it is known that the size of work area for processing the DL exceeds the predetermined size, the DL formed so far is rendered once so as to form a raster image and the DL formed so far is cleared once.
The raster image is added again as a background image of a drawing area to a part of the DL.
Ordinarily, since the background image is compressed, a size of DL which is added is smaller than the original DL size. Therefore, by forming the residual DL into the empty area, the DL of a large size can be processed in the limited memory space. Since the work area of the renderer is also cleared when the rendering is finished at the time of fallback, the size limitation of the work area can be also avoided and the printing apparatus of a low cost can be provided. For example, refer to Japanese Patent Application Laid-Open No. H7-137355.
Although the raster image formed in the step of executing the fallback process as mentioned above is compressed and added to a DL list, the compression image which is formed at this time has to be also enclosed in the predetermined size.
Particularly, since the size of raster image which is formed upon rendering in the case of a color image is very large and, in many cases, the compression image cannot be enclosed in the predetermined size at the time of reversible compression, irreversible compression is ordinarily used.
However, if the irreversible compression is used, the compressed image deteriorates. There is, consequently, a problem such that if the deteriorated compression image is used as a background image and a residual foreground image is drawn thereon, a difference of picture quality is caused between the foreground image and the background image, so that its boundary becomes conspicuous.
FIG. 9 is a diagram for explaining an example of a print result which was irreversible-compression processed in the conventional printing apparatus.
In FIG. 9, reference numeral 301 denotes a print result. For example, the side over a position 310 corresponds to the background image and a side under the position 310 corresponds to the foreground image. There is a problem such that since a difference of the picture quality is large, only a print result of low quality in which a boundary between the background image and the foreground image is clearly conspicuous can be obtained due to a difference of the picture quality between the foreground image and the background image.